1. Field of the Invention
The present invention is concerned with a novel process for the manufacture of 3-hydroxy-2,6,6-trimethyl-2-cyclohexen-1-one, a key compound in canthaxanthin syntheses, by the isomerization of an epoxide.
2. Brief Description of the Related Art
Isomerizations of epoxides to carbonyl compounds in the presence of Lewis acids have been known for a long time. Because these reactions are often technically unsatisfactory with respect to yields and/or reaction conditions, the use of noble metal catalysts has also been investigated for some time.
Isomerizations of .alpha.-.beta.-epoxyketones to .beta.-diketones in the presence of palladium (O) catalysts are described in Japanese Kokai No. 81/15216 and in J. Amer. Chem. Soc. 102. 2096 (1980). However, epoxyketones having an .alpha.-alkyl substituent generally react only sluggishly according to the stated process and give only low yields of .beta.-diketone after relatively long reaction times.